Certain types of portable AM/FM radios are designed specifically to cope with harsh environmental conditions at construction work sites and the like. Such “worksite” type radios may typically be driven by a switched mode power supply with a relatively higher power rating than traditional household radios so as to enable audio to be broadcast through the speakers across a wider and/or noisier (typically outdoors) worksite environment. It is also generally required that the switched mode power supply has a higher power rating than traditional household radios so that it can be used to charge up worksite power tools via an output power jack on the radio.
One problem with worksite type radios is that the switched mode power supply tends to generate electromagnetic radiation which interferes with and degrades operation of the radio tuning circuit and hence the quality of audio that is output by the radio. The extent of the interference increases proportionally with the power rating of the switched mode power supply. In seeking to address this problem, electromagnetic shielding has been used in certain worksite radios to reduce the tuning circuit's exposure to the effects of electromagnetic interference. However this approach has limitations as electromagnetic radiation may still travel through connection cables of the switched mode power supply resulting in interference with neighbouring electronics including the tuning circuit. Alternatively, attempts have been made to utilise power supplies comprising linear transformers which work on AC-line frequencies of 50/60 Hz as they do not tend to generate electromagnetic radiation that interferes with the AM/FM radio spectrum. Unfortunately, these AC-line type power supplies have relatively poor power efficiency compared to a switched mode power supplies, and, the size and weight of the linear transformer in the AC-line type power supply required to provide suitable power rating of the worksite type radio needs to be relatively large and heavy.